C Program to Find and Print Common Elements from Two Array

In this tutorial, we will learn about how to create a program that allows user to enter any 10-10 array elements for two arrays, and then put all the common elements from both the array in third array. Here we have to put common elements in third array without putting any duplicate element. Finally print the value of third array as output.

Find Common Elements from Two Arrays in C

The question is, write a program in C that read 10-10 elements for two arrays say a[10] and b[10] from user and then put common elements from both the array in third array without putting any duplicate element, then print the value of third array. The program given below is the answer to this question:

#include<stdio.h>
#include<conio.h>
int main()
{
    int a[10], b[10], c[10], i, j, k=0, x, count;
    printf("Enter 10 elements for array A: ");
    for(i=0; i<10; i++)
        scanf("%d", &a[i]);
    printf("Enter 10 elements for array B: ");
    for(i=0; i<10; i++)
        scanf("%d", &b[i]);
    for(i=0; i<10; i++)
    {
        for(j=0; j<10; j++)
        {
            if(a[i]==b[j])
            {
                count = 0;
                for(x=0; x<k; x++)
                {
                    if(a[i]==c[x])
                        count++;
                }
                if(count==0)
                {
                    c[k] = a[i];
                    k++;
                }
            }
        }
    }
    printf("\nArray C (Contains Common Elements from two given Array):\n");
    for(i=0; i<k; i++)
        printf("%d ", c[i]);
    getch();
    return 0;
}

As the above program was written under Code::Blocks IDE, therefore after successful build and run, here is the sample run that you will also get on your output screen. Here is the first snapshot of the sample run:

Now supply any 10 array elements for both the array and then press ENTER key to see the common elements from both the array as output as shown here in the second snapshot of the sample run:

Here are some of the main steps used in above program:

• Receive any 10 elements for first array say a[10]
• Again receive any 10 elements for second array say b[10]
• Create a for loop that runs from 0 to 9
• Inside this, create another for loop that also runs from 0 to 9
• We have created two for loop here, to compare each and every element of first array to each and every element of second array
• The two for loop here is created in the way that 0^th element of first array is compared with all the 10 elements of second array, then 1^st element of first array is compared with all the 10 elements of second array, ..., 9^th (last) element of the first array is compared with all the 10 elements of second array
• Inside the inner for loop, use if statement to check whether the current element of both the array is equal to each other or not
• If it is, then again check whether this element is already present inside the third array say c[] or not
• If it is, then increment the value of any variable say count to check later, whether count holds it original value that is 0 or not
• If it holds its original value then we have to put the current element inside the third array, otherwise if count has some value, then it means that the current element already exists inside the third array
• As we have not to put any duplicate element, then continue to check for the next match
• After putting all the matching element from both the array (without any duplicate element) come out from both the for loop
• At last print the value of third array that shows all the common elements from both the given array

Let's modify the above program and allow the user to provide the size for both the array along with its elements. Then put the common elements in third array without any duplicate element. Finally print out all the three array as output. Here is the program:

#include<stdio.h>
#include<conio.h>
int main()
{
    int a[50], b[50], c[50], i, limitA, limitB, j, k=0, x, count=0;
    printf("How many element you want to store in array A: ");
    scanf("%d", &limitA);
    printf("How many element you want to store in array B: ");
    scanf("%d", &limitB);
    printf("Enter any %d array elements for array A: ", limitA);
    for(i=0; i<limitA; i++)
        scanf("%d", &a[i]);
    printf("Enter any %d array elements for array B: ", limitB);
    for(i=0; i<limitB; i++)
        scanf("%d", &b[i]);
    for(i=0; i<limitA; i++)
    {
        for(j=0; j<limitB; j++)
        {
            if(a[i]==b[j])
            {
                count=0;
                for(x=0; x<k; x++)
                {
                    if(a[i]==c[x])
                        count++;
                }
                if(count==0)
                {
                    c[k]=a[i];
                    k++;
                }
            }
        }
    }
    printf("\nArray A:\n");
    for(i=0; i<limitA; i++)
    {
        if(i==(limitA-1))
            printf("%d", a[i]);
        else
            printf("%d, ", a[i]);
    }
    printf("\n\nArray B:\n");
    for(i=0; i<limitB; i++)
    {
        if(i==(limitB-1))
            printf("%d", b[i]);
        else
            printf("%d, ", b[i]);
    }
    printf("\n\nArray C:\n");
    for(i=0; i<k; i++)
    {
        if(i==(k-1))
            printf("%d", c[i]);
        else
            printf("%d, ", c[i]);
    }
    getch();
    return 0;
}

The program was build and run under Code::Blocks IDE, here is the first snapshot of the sample run:

Let's provide the size and elements for both the array, press ENTER key to see both the array along with third array that contains the common elements from both the given array as shown in the second snapshot of the sample run here:

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